420, , or 4/20 (pronounced four-twenty) is a code-term in cannabis culture that refers to the consumption of cannabis, especially smoking cannabis around the time p.m. The Waldos referred to this plan with the phrase " Louis".

(or in 24-hour notation) and smoking and celebrating cannabis on the date April 20 (which is 4/20 in U. Several failed attempts to find the crop eventually shortened their phrase to simply "", which ultimately evolved into a codeword that the teens used to mean marijuana-smoking in general.

However relocation might be required in some cases due to issues such as environmental protection.

The growing size of the unofficial event at UC Santa Cruz caused the Vice Chancellor of Student Affairs to send an e-mail to parents in 2009 stating: "The growth in scale of this activity has become a concern for both the university and surrounding community." Signs bearing the number "420" have been frequently stolen.

Vivian Mc Peak, a founder of Seattle's Hempfest states that 4/20 is "half celebration and half call to action".